If ARCH_HAS_READ_CURRENT_TIMER is not defined and on current timer is used for udelay, then __loop_delay and __loop_const_udelay is used to delay a specific time interval. but in delay-loop.S, loops_per_jiffy (not per cpu data) is used to calculate the number of loops. in SMP system, udelay delays the wrong time interval if two cpus running at different frequency. In arch/arm/lib/delay.c arm_delay_ops is set to arm_delay_ops. /* * Default to the loop-based delay implementation. */ struct arm_delay_ops arm_delay_ops = { .delay = __loop_delay, .const_udelay = __loop_const_udelay, .udelay = __loop_udelay, }; -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html